This invention relates to interconnection schemes for use primarily with telecommunication devices. More particularly, this invention relates to an electrically balanced connector assembly.
Communication system and/or network efficiency is directly dependent upon the integrity of the connector scheme employed. Such connector schemes include, for example, standard interfaces for equipment/user access (outlet connector), transmission means (horizontal and backbone cabling), and administration/distribution points (cross-connect and patching facilities). Regardless of the type or capabilities of the transmission media used for an installation, the integrity of the wiring infrastructure is only as good as the performance of the individual components that bind it together.
By way of example, a non-standard connector or pair scheme may require that work area outlets be rewired to accommodate a group move, system change, or an installation with connecting hardware whose installed transmission characteristics are compatible with an existing application but are later found to have inadequate performance when the system is expanded or upgraded to higher transmission rates. Accordingly, connecting hardware without properly qualified design and transmission capabilities, can drain user productivity, compromise system performance and pose a significant barrier to new and emerging applications.
Reliability, connection integrity and durability are also important considerations, since wiring life cycles typically span periods of ten to twenty years. In order to properly address specifications for, and performance of telecommunications connecting hardware, it is preferred to establish a meaningful and accessible point of reference. The primary reference, considered by many to be the international benchmark for commercially based telecommunications components and installations, is standard ANSI/EIA/TIA-568 (TIA-568) Commercial Building Telecommunications Wiring Standard. A supplement Technical Systems Bulletin to TIA-568 is TIA/EIA TSB40 (TSB40), Additional Transmission Specifications for Unshielded Twisted-Pair Connecting Hardware. Among the many aspects of telecommunications wiring covered by these standards are connecting hardware design, reliability and transmission performance. Accordingly, the industry has established a common set of test methods and pass/fail criteria on which performance claims and comparative data may be based.
To determine connecting hardware performance in a data environment, it is preferred to establish test methods and pass/fail criteria that are relevant to a broad range of applications and connector types. Since the relationship between megabits and megahertz depends on the encoding scheme used, performance claims for wiring components that specify bit rates without providing reference to an industry standard or encoding scheme are of little value. Therefore, it is in the interest of both manufacturers and end users to standardize performance information across a wide range of applications. For this reason, application independent standards, such as TIA-568 and TSB40, specify performance criteria in terms of hertz rather than bits. This information may then be applied to determine if requirements for specific applications are complied with. For example, many of the performance requirements in the IEEE 802.3i(10BASE-T) standard are specified in megahertz, and although data is transmitted at 10 Mbps for this application, test "frequencies" are specified in the standard (as high as 15 MHz).
Transmission parameters defined in TSB40 for unshielded twisted pair (UTP) connectors include attenuation and near-end crosstalk (NEXT) and return loss.
Connector attenuation is a measure of the signal power loss through a connector at various frequencies. It is expressed in decibels as a positive, frequency dependent value. The lower the attenuation value, the better the attenuation performance.
Connector crosstalk is a measure of signal coupling from one pair to another within a connector at various frequencies. Since crosstalk coupling is greatest between transmission segments close to the signal source, near-end crosstalk (as opposed to far-end) is generally considered to be the worst case. Although measured values are negative, near-end crosstalk (NEXT) loss is expressed in decibels as a frequency dependent value. The higher the NEXT loss magnitude, the better the crosstalk performance.
Connector return loss is a measure of the degree of impedance matching between the cable and connector. When impedance discontinues exist, signal reflections result. These reflections may be measured and expressed in terms of return loss. This parameter is also expressed in decibels as a frequency dependent value. The higher the return loss magnitude, the better the return loss performance.
Since connecting hardware is generally considered to be electrically short relative to signal wavelengths, return loss requirements are only applied to products that have lengths of internal wiring or circuitry of six inches or more (such as patch panels).
The net effect of these parameters on channel performance may be expressed in signal-to-noise ratio (SNR). For connecting hardware, the parameter that has been found to have the greatest impact on SNR is near-end crosstalk.
Several industry standards specify multiple performance levels of UTP cabling components have been established. For example, Category 3, 4 and 5 cable and connecting hardware are specified in EIA/TIA TSB-36 & TIA/EIA TSB40 respectively. In these specifications, transmission requirements for Category 3 components are specified up to 16 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 10 Mbps, such as 4 Mbps Token Ring and 10BASE-T.
Transmission requirements for Category 4 components are specified up to 20 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 16 Mbps, such as Token Ring.
Transmission requirements for Category 5 components are specified up to 100 MHz. They are expected to support UTP voice as well as emerging video and ANSI X3T9 series data applications with transmission rates up to 100 Mbps, such as 100 Mbps Twisted-Pair Physical Media Dependent (TP-PMD).
In order for a UTP connector to be qualified for a given performance category, it must meet all applicable transmission requirements regardless of design or intended use. The challenge of meeting transmission criteria is compounded by the fact that connector categories apply to worst case performance. For example, a work area outlet that meets Category 5 NEXT requirements for all combinations of pairs except one, which meets Category 3, may only be classified as a Category 3 connector (provided that it meets all other applicable requirements).
It is recognized that there are numerous ways of achieving electrical balance for connecting hardware of the type that is disclosed by the present invention. Several Category 5 type outlet connectors are presently commercially available. These include Systemax SCS Category 5 Products from AT&T Network Systems, DVO Plus and BIX Plus from Northern Telecom and the Category 5 ACO outlet from AMP. This list is only exemplary and is not intended to be a complete listing of Category 5 type products that are presently commercially available. Accordingly, there is a continuing need for improved outlet connectors which meet or exceed Category 5 performance requirements in order to satisfy increasing bandwidth requirements of communication systems and networks.
The Systemax SCS Category 5 outlet from AT&T network systems uses a "cross-over lead" concept which achieves a desired level of crosstalk performance without the use of printed wiring boards or other additional components. This product uses a variation of the well known lead-frame outlet construction that has been in use for many years by numerous companies. Although this approach offers potential cost benefits by minimizing the quantity and types of components in the completed assembly, it is limited in several major respects. First, because of its completely custom design, the multiple outlet configurations that are presently in use in the industry, of which a minimum of twenty-four exist as defined by the T1E1.3 Working Group on Connectors and Wiring Arrangements, cannot be accomplished without the expense of re-tooling each of the individual configurations in order to accommodate their unique interface and connection schemes. Another limitation of the AT&T SCS outlet is that, because the outlet contacts are physically integral to the product's wire termination means, its ability to connect electrical components, such as fuses, in series or parallel with individual circuit elements is not possible. The custom design of this product also makes it necessary to provide it with special tools or other components that are specifically designed to terminate individual UTP conductors, since the connection points are not compatible with tools that are common to the industry or trade.
Because of its printed circuit construction, the Category 5 ACO outlet offered by AMP Incorporated, overcomes some of the limitations listed above for the AT&T product, but is encumbered by several severe limitations of its own. The method used to correct for the electrical imbalance of the outlet connector involves a combination of individual discrete capacitors that are soldered onto the circuit board and capacitive pads that are etched into the top and bottom surfaces of the board itself. These capacitors compensate for the reactive imbalance between wire pairs, which in-turn improves the product's crosstalk performance. The limitation of this approach is that it requires additional expense for the discrete capacitors and for the secondary operations required to locate and solder them into place.
Since telecommunications outlets require two types of connections, there are two types of connectors that must be mounted on the circuit board. One type is the outlet connector that is, directly accessible when the outlet assembly is mounted in a standard electrical box. The other type is comprised of means to connect the outlet to individual wires in order to provide access to the telecommunications network. This second type of component is most often placed behind a faceplate or other physical barrier to conceal and protect the wire connections during normal use. Because one type of connector is intended to be accessible once installed, and the other is not, it is often preferable that they be mounted on opposite sides of the circuit board.
Such opposed-surface mounting provides the benefits physical isolation between the two connection means and is more space efficient, but opposed surface mounting requires two separate soldering operations for prior-art outlets, the second of which must be manual unless the components are all made of special, high-cost materials that are able to withstand the extreme temperatures of vapor-phase soldering. For this reason, the AMP ACO outlet and other known prior-art telecommunications outlets that employ printed circuitry are designed with components that are soldered from the same side of the printed circuit board.
The BIX Plus Category 5 telecommunications outlet offered by Northern Telecom, Inc. also employs printed circuitry to improve the balance between pairs. In order to achieve a higher level of crosstalk performance this product relies on capacitive pads that are etched into opposed sides of the printed board. A significant drawback of this approach is that, in order to add sufficient capacitance to improve performance to achieve Category 5 performance for some circuits, it may be necessary to enlarge the pads to a size that compromises space efficiency and printed circuit board cost.
If the spacing between the pads is reduced by making the printed circuit board thinner, mechanical integrity is reduced and the board may no longer be compatible with off-the-shelf circuit-mounted components that are designed for a standard board thickness. In addition, the use of etched circuit pads has inherent limitations on the accuracy and consistency of their capacitance due to the inherently wide manufacturing tolerances (typically .+-.10%) on circuit board thickness.
The BIX Plus Category 5 outlet shares many of the other limitations of the AMP ACO product. Since all components are mounted on the same side of the circuit board, it has similar limitations with respect to space efficiency and the routing of wires within the electrical box. In addition, because the components are oriented such that they are all accessible from the front, the height of the wire termination connector mandates that a non-standard, high profile outlet connector be used to provide unencumbered access with a modular plug.
It will be appreciated that other methods of balance compensation exist, such as selective parallel runs of circuit traces either in a side-by-side configuration or overlapping traces placed on adjacent layers of a circuit board. It is also possible to vary trace thickness in order to achieve a degree of inductive balance correction between pairs. Yet another method of achieving balance between pairs that employs neither lead-frame or printed circuit construction is to selectively twist wire leads that exit the back of a conventional modular jack outlet. However, each of these methods has its own inherent limitations in terms of repeatability, cost and performance.
A significant physical limitation that is shared by each of the above-described telecommunications outlets is the orientation of the outlet opening. Because the cables that these products are designed to connect-with have high performance characteristics, it is also important that the physical integrity of the cable be preserved to the greatest extent possible. For this reason, TIA specification TSB40 requires that, in spaces with UTP terminations, cable bend radii shall not be less than eight-times the cable diameter. For standard four-pair UTP cable, this requirement translates to a minimum bend radius of not less than 40 millimeters (1.5 inches). The direct outward orientation of the prior-art Category 5 outlets requires that, for nearly all wall mounted applications, the plug cord take an immediate right-angle bend as it exits the outlet. The ever-present effect of gravity naturally causes the bend radius to tighten, which may or may not be compounded by the presence of furniture directly in front of the outlet opening. These factors make it difficult, if not impossible for the prior art Category 5 outlets to prevent the plug cable from violating the bend radius requirements of industry standards. Therefore, the prior art devices are physically unable to consistently provide the level of performance that is required for this type of connector.
Other telecommunications outlets, particularly those that mount directly to a flat surface, as opposed to a recessed electrical box or other enclosure, provide outlet openings that have a substantially perpendicular orientation to the wail. One such outlet is manufactured by Cekan A/S of Denmark. A disadvantage of these products is that they do not offer recessed electrical box mounting and that they do not offer a comparable level of transmission performance.
Prior art connectors that do have the substantially perpendicular orientation such as the one offered by Cekan have an additional limitation. Since they are often mounted on a baseboard, which is directly adjacent to the floor surface, the outlet opening is susceptible to contaminants such as corrosive solvents that may wash into the jack during cleaning. Also, solid debris such as dust, lint and dirt are free to enter and cause damage to the outlet receptacle.